Printing machines are known that print curved surfaces with drop-on-demand inkjet print heads. Usually, in this method, colors are printed consecutively as cyan (C), magenta (M) and yellow (Y) with black (K) onto the object with the curved surface moved relative to the inkjet print heads to create the color impression and/or the colored print image on that surface. For transparent subsurfaces, e.g. bottles made of plastic or glass, usually a base color layer is printed first, often in white, in order to create better opacity. Basically, other colors may be used for this as well which basically may also contribute to the graphic print image of the color layer.
U.S. Pat. No. 8,522,989 B2 describes digital printing of three-dimensional bodies with particularly a curved surface during which a base layer is at least partially applied onto the three-dimensional body. This base layer may be transparent or opaque. On this base layer, additional elements such as labels can be printed for the graphic design. This creates a three-dimensional effect that makes the label stand out from the base layer. As a further design element, a type of inverse printing is described that leaves specially formed gaps free during the printing of the base layer. This creates an effect through which the elements created due to the missing base layer seem to be set back compared to the base layer. The base layer that differs in particular in color and/or in its thickness/brightness from the three-dimensional object is therefore consciously used for contrasting design elements according to the teaching of U.S. Pat. No. 8,522,989 B2. The margins of the base layer and/or the print application are consciously intended to create a three-dimensional effect and be visible.
This is, however, a disadvantage if the basically, for example, transparent three-dimensional object should not receive an extensive, for example opaque base color layer because the view of the product contained in the object should be maintained. This is, for example, often the case for transparent beverage bottles if those should only be printed with a label or an inscription, possibly in several colors, or the three-dimensional object should not be coated anywhere else than the print image (print area) for other reasons, e.g. because of a particularly high-quality surface. In such cases it is not desired that the base color layer (that usually has a different color, especially white) shines through on the margins of the print image. This effect in particular occurs due to the relative movement between the surface of the three-dimensional object to be printed and the ink drop that hits this surface.
In some circumstances, that relative movement may be quite large. Those objects are rotated at a high speed in front of the inkjet print heads working with the drop-on-demand method in printing machines made for printing rounded, especially cylindrical, objects such as, preferably, bottles or cans to which the method suggested according to an embodiment of the invention refers in particular. The consequence is that the drop on the surface is not circular and round and, e.g. flows evenly over the margin of a previously applied layer, e.g. the base color layer, covering its margin, but is smudged against the relative movement, and consequently distorts. On the surface, the resulting contours are shaped more like a drop. This is not pleasant because, in this case, especially in case of a basically color-neutral first white print that does not influence the printed color with a color cast, because there is a “flash” of the color white on the margin of the print image. The white (or differently colored) first base color layer is visible underneath the actual color.
This is visible in FIG. 1, which schematically shows the print 11 on a three-dimensional object 12 as the result of a traditional print method. For improved ink adhesion, a primer 13 has been applied directly on the surface of the object 12 as an adhesive primer. On the primer 13, the (especially white) first base color layer 14 has been applied, which is then printed with the color layer 15 in several colors during several printing runs as a structured print image. The color layer is protected by a coating 16 in the sense of a varnish and/or top coat. On the sides indicated with an arrow, the white (or differently colored) base color layer 14 is visible underneath the actual color.
It is furthermore known that in the case of different materials underneath the base color layer, an adhesive base usually referred to as primer is printed or otherwise applied. In addition, a coating, also referred to as varnish/top coat in the sense of a coating varnish in order to generate certain characteristics, may be printed or otherwise applied after the printing of the three-dimensional object with the actual print image. This coating is intended to protect the print image against damage. The coating is usually a varnish paint, but may also consist of a different material according to an embodiment of the invention, e.g. a transparent and preferably also color-neutral plastic layer in the sense of a plastic coating. The primer 13 and the coating 16 are also depicted in FIG. 1.
All these applications and/or layers, especially print layers applied with print methods, share the characteristic that they are directly copied by the print image, especially with regard to their size, i.e. their dimensions. This results in print images with a common size and dimensions on the three-dimensional, curved surfaces for each applied layer, which are printed one over the other. The disadvantage of the traditional application of the individual applied layers is, therefore, that the margins of the individual application layers are free and not only visible, but also in an area where they are vulnerable to exterior influences
DE 44 38 536 A1 discloses a method for the sectional coating of a transparent carrier plate with an active layer applied in a roll stamping procedure. In this process, a protective layer is applied to the active layer and other layers, if applicable, so that the active layer and the possible further layers in those areas are resistant against chemical etching. During an etching process the active layer and the possible further layers are etched away only in the area not covered by the protective layer, and the protected area remains.
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